Correlation of the onshore and offshore stratigraphy of Vietnam using zircon U-Pb dating and provenance analysis

Correlation of the onshore and offshore stratigraphy of Vietnam using zircon U-Pb dating and provenance analysis

Tim Breitfeld, Juliane Hennig, Amy Gough & Robert Hall

Aims
This project will focus on the age, character, and tectono-stratigraphical evolution of the southern South China Sea and the Indochina-East Malaya block in Vietnam using petrological and geochronological studies. U-Pb zircon dating of igneous and sedimentary rocks will be used to identify distinctive zircon age populations of the regional basement. These, in combination with heavy and light mineral modes, will be used to get a better understanding of sedimentary pathways in the region and ultimately provide further insights into the development of hydrocarbon-bearing basins in the South China Sea region.

Background
Vietnam forms part of the Indochina-East Malaya block, which was separated from Gondwana in the Devonian and formed part of Cathaysialand during the Permian (Metcalfe, 1996, 2009, 2011a). In the Early to Middle Permian the Sibumasu terrane separated from Gondwana and later collided with Cathaysialand in the Late Triassic to Early Jurassic (Metcalfe, 2009). Triassic granitoids form a Mesozoic basement which is overlain by Jurassic and Cretaceous sediments, such as the Dray Linh, La Nga and the Ban Don Formations (Jurassic) and the Dak Rium and Don Duong Formations (Cretaceous). Their ages are poorly dated so far and based on biostratigraphy, stratigraphic relations, and limited Rb-Sr and K-Ar dating. The sedimentary rocks are intruded by Mesozoic granitoids that are subdivided into three plutonic suites; the Deo Ca and the Dinhquan suites, both of which are Middle Cretaceous in age (between 118 Ma and 115 Ma), and the Ankroet suite, which was emplaced in the late Cretaceous, around 87 Ma (Shellnutt, 2013). The uppermost part of the stratigraphy in the Da Lat Zone is formed from Cenozoic basalts. The Proto-South China Sea formed as an ocean basin between the Indochina-East Malaya block and Borneo in the Cenozoic (Rangin et al., 1990; Hall, 2002).

Subduction beneath northern Borneo started in the Early Oligocene and resulted in extension the subsequent opening of the South China Sea from the Oligocene to Miocene (c. 32 Ma to 20.5 Ma) (Barckhausen & Roeser, 2004; Barckhausen et al., 2014). There are ongoing debates about the tectonic evolution of the South China Sea, Proto-South China Sea, and the timing of regional unconformities in the area. Subsidence of the South China Sea during the Paleogene and Neogene, related to further extension, led to the development of large sedimentary basins such as the Cuu Long and Nam Con Son Basins offshore from South Vietnam. These basins contain thick Paleogene to Neogene fluvio-deltaic to shallow or deep marine sedimentary sequences (Matthews et al., 1997). Mesozoic granitoids of the Da Lat Zone are thought to represent the basement in the area, and are considered as possible sediment sources.